The invention relates to radio communication systems which transmits a signal from one point to another over a certain distance. The signal received at the receiving end is often subject to fading and distortion due to environmental effects. The problem called the multipath effect is particularly acute for digitally modulated signals. The multipath effect means that the signal transmitted from a transmitter can travel to the receiver through a direct path and through an indirect path which varies with environmental conditions. As a result the signal which is detected at the receiving end can fade over time, and/or the same signal may received at two different times due to the difference in time that it took for the signal to travel the indirect path versus the direct path.
The problem created by the multipath effect can be partially cured by receiving the same signal at two different physical locations and then combining the two signals to create a composite output. The multipath effect varies from location to location. While one location is experiencing a multipath fading effect, another nearby location may experience no problem at all. Therefore if you receive the same signal at two different locations, chances that both are experiencing a multipath fading effect at the same moment is fairly low. By combining the signals received from two different locations and creating a composite output, the effects of multipath fading can be greatly reduced.
To get a single composite signal from two antennas from diverse locations, you must have a way to either select one of the two signals or combine the two signals to create a composite output. It is known in the art to base a decision of which signal to select on the signal strength or on the amplitude to frequency signal dispersion. It is also known to use the phase difference between the two signals which are received at the two diverse locations to decide whether or not to combine the two signals. None of the prior art has provided a low cost combiner system which operates in the intermediate frequencies which bases its decision on whether or not to combine or to select a signal on the signal strength and the amplitude to frequency dispersion in which also uses a phase detector to bring the two signals into phase alignment.
It is accordingly an object of the present invention to provide an intermediate frequency combiner system for use in a space diversity radio receiver where the decision of which signal to select or whether or not to combine two signals is based on the signal strength and the amplitude to frequency dispersion.
It is a further object of the present invention to provide a phase detector and a phase correction system so that the two signals are brought into phase alignment prior to combination and prior to squelching of one of the signals.
It is yet a further object of the present invention to provide a method of selecting or combining intermediate frequency signals which have been received at diverse locations such that a better signal output is provided than would have been obtained from simple combination of the two signals.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.